More On Basic RV Electricity

Mark J. Polk

I received quite a few questions and comments on last month’s article, “Basic RV Electricity.” The questions and comments were very good and they addressed some RV electrical concerns I didn’t cover in the article. I thought that everyone could benefit from this information and decided to include it this month.

Question: “What is a deep cycle battery?”

Answer: RVs come equipped with deep cycle batteries for the coach. Most RVs come with a single Group 24 deep cycle battery. Deep cycle batteries are rated in amp/hours. How many amps the battery can deliver for how many hours before the battery is discharged. Deep cycle batteries are designed to be discharged over and over again and still take a charge. If you enjoy dry camping (without hook-ups) you depend on your deep cycle battery(s) to take care of your 12-volt needs. You can purchase a deep cycle battery with a higher amp/hour capacity that will last longer. The higher the amp/hour capacity is the larger the battery is. If you have room for a larger battery and enjoy dry camping you may want to consider a Group 27 or Group 31 deep cycle battery.

Comment: “You did not cover inverters. I installed one in my motorhome because there are times when you want a little power for the TV or VCR and don’t want to crank the generator.”

Reply: You are absolutely right. Inverters are nice to have at times when you are dry camping and/or when you don’t have access to 120-volts AC. Batteries produce power in Direct Current (DC) that run at low voltages. Power companies and AC generators produce sine wave Alternating Current (AC), which is used to operate 120-volt appliances and electronic equipment. An inverter takes 12-volt DC power from your RV batteries and electronically changes it to 120-volt AC. Some RVers use an inverter just to watch TV or for their personal computer. Other RVers use an inverter to operate microwaves, coffee pots or other larger appliances. When you purchase an inverter the inverter’s output capacity must be capable of operating the loads that will be placed on it.

Inverters have two different capacity ratings. Continuous output rating and surge capacity rating. Continuous output is the maximum wattage the inverter can output for a long time period. Surge capacity is the maximum wattage the inverter can output during initial start up. All appliances require more power when they start, compared to what they use when they are running. They can use as much as two or three times the amount to start then what they use to run, so the starting power required for any appliance that you plan to use with the inverter must be within the surge capacity rating. There are modified sine wave inverters and true sine wave inverters. A true sine wave inverter is more expensive, but they are capable of producing power as good as the power company and all appliances and electronic equipment will run as they are intended to. Keep in mind you are drawing the power from your RV batteries and any power used has to be put back in through some type of effective charging system.

Comment: This is a second comment from the same reader. “You need to tell your reader’s what to do when you only have 15 amps to plug in to, (usually at someone’s home and using the plug on their front porch) and you need the air conditioner.”

Reply: I personally don’t recommend doing this, but I agree that it is possible, like you say to use the A/C if you are plugged in to a 15-amp outlet. If you do, you must exercise caution. When the A/C compressor engages it requires more amps (about 13) than it does once it is running. Because of this you need to turn all appliances off before starting the A/C, to include switching the refrigerator from A/C to LP gas. Once it is running it may be possible to use a small appliance or electronic equipment that operates on low amperage, like a TV, but you need to monitor the voltage to prevent damaging any appliances or electronic equipment.

Comment: This is the third comment from the same reader. “You should also tell your reader’s that if they are using a long extension cord it must be #12 wire or lower, (heavier gauge) to keep the amount of voltage drop from causing problems.”

Reply: You’re right again. If it is possible you should try to avoid using an extension cord when making electrical connections at the campground. The gauges of the wire used in standard household extension cords are not suitable for RV electrical hook-ups. Eventually you will be put in a situation where you will need to use an extension cord. It is a good idea to purchase an RV extension cord that is compatible to the electrical system of your RV, and have it on hand. If you do purchase an extension cord somewhere else I recommend 10-guage wire and use as short of a cord as possible.

Question: “Will it hurt to leave the RV plugged in and the refrigerator on all of the time?”

Answer: I leave my refrigerator on almost all of the time. The RV should be on level ground so the refrigerator operates properly and you will need to monitor it for when it needs to be defrosted. The only other concern with leaving the RV plugged in, not related to the refrigerator, is the coach battery. Whenever the RV is plugged in the coach battery is being charged. It's really just a trickle charge, but over time it can deplete the electrolyte levels in the battery cells. You need to check, or have somebody check the battery at least monthly when the RV is plugged in during storage.

Question: “Is there any danger of damaging your system if you plug a 30-amp system into a 50-amp service using the proper adapter?”

Answer: This is a controversial subject. Some people will argue that if they make an electrical adapter for it than it is safe. Others will argue that it is not safe to use a 50-amp service for a system designed for 30-amps or a 20-amp service for a 30-amp system. Electrical adapters are a necessity for RVers. Eventually you will be in a situation where you have to use some type of electrical adapter to make a connection at a campground. It may be an outdated campground or isolated area that only provides 15 or 20-amp electrical service, or the only site available is a 50-amp service for your 30-amp system. There are adapters that will go from your RV type plug and size down to household type outlets and adapters that go from household type outlets to all types of campground RV connections. It’s nice to have these adapters on hand when you need them, but you must exercise caution and use common sense when you use them. If you have a 30-amp system and you have to use a 50-amp service use your RV electrical system exactly the same way you do when you’re plugged into a 30-amp service. In other words don’t try to run anymore than you normally would. On the other hand if your RV is a 30-amp or 50-amp system and you use an adapter to plug the RV into a 15 or 20-amp outlet you severely limit what you can operate in the RV. In this situation you should only use what appliances or electronic equipment are absolutely necessary. If you place too much of a demand on electrical adapters, or use them for extended periods of time they can overheat and melt resulting in damage to the RV power cord or the electrical system.

Question: “Sometimes the coach battery in our motorhome won’t start the generator and other times it will. My question is why isn’t the RV battery charger keeping my battery charged when I leave it plugged in all the time?”

Answer: The battery charger in the RV converter provides a trickle charge and is only designed to keep the coach battery(s) topped off. It is not designed or capable of recharging a battery that is completely discharged or damaged. The automotive alternator also charges the coach battery when you are driving the RV. I would guess that the alternator is probably charging the battery enough to start the generator sometimes after driving for a while, but the RV battery charger can’t charge it enough to start the generator when it’s plugged in. The constant charging from leaving it plugged in all the time can deplete the electrolyte level in the battery(s) cells. Depending on how often the battery(s) is being charged will determine how often it needs to be checked. You should check the battery(s) at least monthly and if you use the RV on a regular basis and / or you leave it plugged in when you’re not using it you may need to check the battery(s) more often.

I hope these reader’s questions and comments are helpful to you and quite possibly might answer some questions that you had about basic RV electricity.